Why DEET Bugs Mosquitoes

March 13, 2008 -- Got insect repellent containing the chemical DEET? Scientists now know how DEET keeps mosquitoes at bay. And that knowledge could lead to even better bug repellents.

DEET masks the smell that draws mosquitoes to your skin, according to researchers at New York's Rockefeller University.

"For all these years, there were a lot of theories but no consensus on how DEET worked," Leslie Vosshall, PhD, says in a news release. "Does it smell bad to mosquitoes or does it blind them to odors? It was a great unsolved problem."

Vosshall and colleagues at Rockefeller University's laboratory of neurogenetics and behavior solved that problem by studying fruit flies genetically engineered without a certain smell receptor.

Those fruit flies were oblivious to DEET doused on fly food in test tubes. They flocked to the food as if DEET were not there.

In comparison, normal fruit flies with that smell receptor intact made a beeline away from the DEET-laced fly food.

The scientists conclude that DEET dims those smell receptors, making it harder for bugs to smell their bait (which is your skin, in the case of mosquitoes).

DEET doesn't dull all sense of smell in insects; "it just shuts down enough of these receptors to confuse the mosquito or blind it to the odors it finds attractive," Vosshall explains.

Why didn't Vosshall's team study mosquitoes instead of fruit flies? Because there isn't a genetically engineered strain of mosquitoes lacking the smell receptor in question, according to a Rockefeller University news release.

The study appears in Science Express, the advance online edition of Science.